This invention relates to thermoformable laminates and, more particular, to thermoformable laminates having improved sound-absorbing characteristics as well as other desirable characteristics. The laminates are especially suited for making headliners for automobiles.
Laminates used as headlines for automobiles normally comprise a sheet of foamed polymer having a fabric bonded to the side thereof that faces the interior of the automobile. It is generally recognized in the automobile industry that laminates intended for use in making automotive headliners for gas-efficient, compact and subcompact automobiles must have a proper balance of certain characteristics. Specifically, the laminates must have the proper balance of: (1) cost, (2) weight, (3) thickness, (4) sound absorption acoustical performance, (5) moldability and (6) environmental stability. Cost, of course, must be as low as possible. Weight must be kept low as possible so as to provide maximum gas milage. Thickness must vary in order to provide maximum interior headroom while filling the space between the roof bows. Sound absorption acoustical performance should be as high as possible so as to provide the quietest possible ride. Thus, while adding more material (e.g. fabric) to the laminate usually improves the sound-absorbing performance of the headliner, it also adds to the cost, weight and thickness of the laminate. The laminate must also be moldable to a shape (headliner) having certain recessed regions of a minimum gage or thickness. Such minimum gage regions are necessary in order to facilitate installation of the headliner under interior trim where the headliner attaches to the automobile (e.g. along the outer perimeter of the headliner), to accommodate points at which the headliner contacts the automobile, such as roof bows of the automobile and to provide for mounting of interior parts to the headliner such as dome lights, sun visors, etc. The recessed regions are provided during molding of the laminate by means of mechanical pressure which compresses the designated regions to the desired minimum gage. Of course, it is equally important that the molded laminate be capable of retaining the minimum gage recessed regions. Thus, the density of the fabric component of the laminate must be great enough to resist the pressure of the expanding action of the foam component of the laminate during molding, but low enough to be capable of being compressed to the desired minimum gage by the mechanical pressing action of the mold. However, excessive fabric density is undesirable because it reduces the sound absorption performance of the laminate. Lastly, the laminate (headliner) must be environmentally stable, for example, it must not sag when the interior of the car reaches temperatures normally encountered during the summer months., e.g., 85.degree. C.
Thermoformable laminates described in the prior art as being suitable for use in making headliners for automobiles typically comprise a sheet of foamed thermoplastic polymer (e.g. a foamed polystyrene) and a layer of non-woven fabric impregnated with resin bonded to one or both sides of the sheet. While these laminates have certain desirable characteristics, they do not have the proper balance of the above listed characteristics. For example, the laminates have only mediocre sound absorption characteristics because the resin component of the fabric causes the laminate to densify during molding and thereafter reflect rather than absorb sound.